A210720 Primes formed by concatenating n, n, n, n, and 1 for n = 1, 2, 3,....

33331, 99991, 242424241, 404040401, 454545451, 464646461, 494949491, 525252521, 575757571, 737373731, 787878781, 949494941, 1021021021021, 1081081081081, 1091091091091, 1211211211211, 1291291291291, 1481481481481, 1511511511511

Offset: 1

Author

Jonathan Vos Post, Jan 29 2013

Keywords

• nonn
• base
• easy

Comments

This is to four (duplicated strings concatenated) as A210712 is to three (duplicated strings concatenated), and as A210511 is to two (duplicated strings concatenated).

Examples

			a(1) = 33331 because Concat(3,3,3,1) = 3331 which is in A000040.
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A210511, A210712.

Programs

Magma

[nnnn1: n in [1..200] | IsPrime(nnnn1) where nnnn1 is Seqint([1] cat Intseq(n) cat Intseq(n) cat Intseq(n) cat Intseq(n))]; // Vincenzo Librandi, Mar 15 2013

Maple

A210720 := proc(n)
        local p;
        [n,n,n,n,1] ;
        p := digcatL(%) ;
        if isprime(p) then
                printf("%d,",p) ;
        end if;
end proc:
for n from 1 to 400 do
        A210720(n) ;
end do: # R. J. Mathar, Feb 10 2013

Mathematica

Select[Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[n], IntegerDigits[n], IntegerDigits[n], IntegerDigits[1], {}}]], {n, 200}], PrimeQ] (* Vincenzo Librandi, Mar 15 2013 *)
Select[Table[FromDigits[Join[Flatten[IntegerDigits/@PadRight[{},4,n]],{1}]],{n,200}],PrimeQ] (* Harvey P. Dale, Oct 16 2017 *)